The age of your uterus is not an issue. The issue is the age of your eggs. We do day 5 transfers of blastocyst the vast majority of the time, regardless of the age of the patient. Genes from the sperm do not play a role in embryo growth and developement until after day 3. Not all of the good looking embryos on day 3 grow to blastocysts. We cannot tell on day 3 which ones wil grow and ehich ones will not. On day 5, we have more information to select embryos for transfer.Good luck.